The present invention relates to a polytrimethylene terephthalate fiber, as a kind of polyester and, more particularly, to a polytrimethylene terephthalate fiber which is capable of being processed into a wide variety of processed yarns and knitted and woven fabrics and is also suited for use in the field of clothing where characteristic knitted and woven fabrics should be provided.
Polyester fibers composed mainly of polyethylene terephthalate are mass-produced, around the world, as fibers which are most suited for clothing, and the polyester fiber industry is an industry of great importance at present.
On the other hand, polytrimethylene terephthalate fibers (hereinafter referred to as xe2x80x9cPTT fibersxe2x80x9d) have been studied for a long time, but have never been produced industrially. However, a method of producing trimethylene glycol as a glycol component at a low price has recently been discovered and the possibility for industrialization of PTT fibers have been enhanced.
Great hopes are entertained of PTT fibers, which are epochal fibers with merits of both polyester fibers and nylon fibers, and application of PTT fibers to clothing, carpets and nonwoven fabrics has already begun by making use of features thereof.
PTT fibers have been known for a long time and prior arts have been disclosed in Unexamined Patent Publication (Kokai) No. 52-5320 (A), Unexamined Patent Publication (Kokai) No. 52-8123 (B), Unexamined Patent Publication (Kokai) No. 52-8124 (C), Unexamined Patent Publication (Kokai) No. 58-104216 (D), J. Polymer Science: Polymer Physics Edition, Vol. 1, 14, 263-274 (1976) (E), and Chemical Fibers International Vol. 45, April (1995), 110-111 (F).
As is apparent from these prior arts, the features of PTT fibers are physical properties similar to those of nylon fibers, for example, smaller initial modulus than that of polyethylene terephthalate fibers (described in D, E, and F), excellent elastic recovery (described in A, D, and E), large thermal shrinkage (described in B), and good dyeability (described in D). It can be said that the main features of PTT fibers lie in soft feeling, stretching properties and low-temperature dyeability. Taking these features into consideration, PTT fibers are particularly suited for use in the fields of underclothes (e.g. foundation garments, panty stockings, etc.) where PTT fibers are used in combination with spandex fibers, with regard for clothing.
Specific physical properties of PTT fibers are good elastic properties (stretching properties) and the features thereof lie in that the initial modulus is almost fixed even if the orientation and elongation at break of fibers are changed, and that the elastic recovery is high (described in F). This reason is considered that the elastic modulus of fibers depends on that of the crystal.
As described above, these prior arts describe excellent properties or general features of PTT fibers in detail, but these prior arts neither describe nor suggest an optimum range of physical properties for clothing. That is, these prior arts neither describe nor suggest an optimum design of raw yarn physical properties of PTT fibers for clothing or ideal physical properties of PTT fibers in due consideration of balance.
These prior arts neither describe nor suggest that PTT fibers have specific surface properties, that is, the frictional coefficient is generally very high because of the polymer, which can cause yarn breakage and fluff during the production and processing of PTT fibers.
As the method of producing PTT fibers, known publications described above disclose a two-stage process wherein melt-spun fibers are once taken up as a undrawn yarn and then the undrawn yarn is drawn. Unlike PET, PTT has a glass transition point at the temperature close to room temperature, e.g. 30-50xc2x0 C., and crystallization proceeds considerably quickly as compared with PET. When shrinkage of fibers in the undrawn yarn is caused by formation of crystallite and relaxation of orientation of molecules, draw spot, fluff and yarn breakage occur during the drawing, thus making it difficult to produce PTT fibers suited for clothing application in an industrially stable manner. As the method of solving the problems of such a two-stage process, for example, WO-96/00808, Published Japanese Translation No. 9-3724 of the PCT Application and WO-99/27168 suggest a method of continuously performing spinning and drawing in one stage without taking up the undrawn yarn. Fibers produced by continuously performing spinning and drawing are taken up into a cheese-shaped package.
This method of continuously performing spinning and drawing is industrially advantageous because of low cost, but the present inventors"" study makes it clear that the method has a problem that fibers obtained by the one-stage process causes shrinkage in dimension after taking out fibers from the cheese-shaped package. It has become apparent that, since the stress in fibers taken up into the package is released, fibers are freely shrunken (hereinafter this proportion is referred to as a free shrinkage factor) and fibers are shrunken in length by about 3% or more. When fibers have such a large free shrinkage factor, it becomes necessary to knit or weave an additional length corresponding to the proportion of the free shrinkage factor in the production of a knitted or woven fabric with a predetermined finish size, that is, the textile design becomes complicated. The reason why fibers obtained by continuously performing spinning and drawing show such a high free shrinkage factor is not clear, but is presumed as follows: {circumflex over (2)} since fibers are taken up into the cheese-shaped package without releasing the stress applied to-molecules from the molten state to solidification during the formation of fibers, the stress is present in fibers and {circumflex over (2)} the stress is present in fibers because of poor thermal fixation of fibers after drawing.
A stress-strain curve of fibers obtained in case spinning and drawing were performed by the two-stage process and that in case where spinning drawing were performed by the one-stage process are shown in FIG. 1 described below. The curve A in FIG. 1 is a curve obtained in case spinning drawing were performed by the two-stage process, and the curve B is a curve obtained in case spinning and drawing were performed by the one-stage process. One inflection point (indicated by the arrow c) exists in case of the two-stage process, whereas, three inflection points exist in case of the one-stage process.
Accordingly, fibers obtained by the two-stage process are suited-for use as fibers for clothing in view of practical use, though the one-stage process is advantageous in view of the production cost.
For the reasons described above, it is strongly required to develop PTT fibers which are obtained by performing spinning and drawing using the two-stage process in due consideration of an optimum design of raw yarn physical properties for clothing or all balance.
WO-99/39041 discloses a method of improving specific surface properties of PTT fibers. This known method improves the surface properties (frictional coefficient) by coating fibers with a surface finishing agent with a specific composition, and discloses that spinning and drawing can be performed by any of the two-stage and one-stage methods described above, a method of producing a semi-drawn yarn without drawing, and a method of producing a drawn yarn. That is, the publication neither describes nor suggests a difference in free shrinkage properties between PTT fibers obtained by the two-stage and one-stage methods as well as practical problems caused by this difference. Moreover, the publication discloses the method which has an object of improving the surface properties of general PTT fibers having a birefringence of 0.025 or more and is directed to PTT fibers having a wide elongation at break within a range from 25 to 180%, and not only does the publication not describe an optimum-range of physical properties of PTT fibers for clothing, but also it neither describes nor suggests the necessity thereof.
As described above, low elongation at break and high frictional properties of a conventional PTT fiber can cause frequent occurrence of yarn breakage and fluff, thus drastically preventing stable production of fibers, and processing such as false twisting of fibers, production and heat-treatment of knitted fabrics or the like.
A first object of the present invention is to provide a PTT fiber which is less likely to cause yarn breakage and fluff in industrial production and also has physical properties and surface properties sufficient to secure smooth false twisting and knitting/weaving. A second object of the present invention is to provide a method of stably producing the fiber as the first object by performing spinning and drawing using the two-stage process. A further specific object of the present invention is to provide a PTT fiber which satisfies a raw yarn quality level capable of sufficiently withstanding warp knitting, weaving and false twisting to which a high quality level is required. The specific object of the present invention is to design proper physical properties and surface properties in view of production of raw yarn, processing of raw yarn, and evaluation of properties and performances of knitted and woven fabric in the PTT fiber.
The present inventors have found that it is effective to attain the objects of the present invention to adjust the elongation at break of the raw yarn of the PTT fiber within a specific range different from an optimum range of a polyethylene terephthalate fiber and a nylon fiber and to selectively specify frictional properties, thus completing the present invention.
That is, the present invention provides a polytrimethylene terephthalate fiber composed of a polytrimethylene terephthalate comprising not less than 95 mole % of a polytrimethylene terephthalate repeating unit and not more than 5 mole % of the other ester repeating unit and having an intrinsic viscosity of from 0.7 to 1.3, wherein the fiber satisfies the following features (1) to (6):
(1) a degree of crystalline orientation of from 88% to 95%,
(2) a peak value of dynamic loss tangent (tan xcex4) max of from 0.10 to 0.15,
(3) a peak temperature Tmax (xc2x0C.) of dynamic loss tangent from 102 to 116xc2x0 C.,
(4) an elongation at break of from 36 to 50%,
(5) a peak value of thermal stress being between 0.25 and 0.38 g/d, and
(6) a fiber to fiber dynamic frictional coefficient of from 0.30 to 0.50.
The polytrimethylene terephthalate fiber of the present invention can be produced by a method of producing a polytrimethylene terephthalate fiber, which comprises extruding a polytrimethylene terephthalate comprising not less than 95 mole % of a polytrimethylene terephthalate repeating unit and not more than 5 mole % of the other ester repeating unit and having an intrinsic viscosity of from 0.7 to 1.3 at 250 to 275xc2x0 C., solidifying an extrudate with a cooling air, coating the extrudate with a finishing agent, spinning the coated extrudate at a withdrawal speed of from 1000 to 2000 m/min, taking up an undrawn yarn once, and then drawing the undrawn yarn, wherein the method satisfies the following conditions (a) to (c):
(a) the undrawn yarn is coated with the finishing agent so that a fiber to fiber dynamic frictional coefficient of the fiber after drawing and heat-treatment is from 0.30 to 0.50,
(b) the coated undrawn yarn is drawn at a draw tension from 0.35 to 0.7 g/d, and then
(c) the drawn yarn is subjected to stretch heat-treatment at the temperature of from 100 to 150xc2x0 C.